This study focuses on investigating fixed and transient factors related to the risk for upper extremity (UE) laceration injuries in meatpacking workers because 1) high rates of UE trauma and associated economic costs have been well documented in the US workforce; 2) existing data suggest high rates of UE trauma in meatpacking workers, although little empirical data are available on risk and causal factors; and 3) our prior experience in studying meatpacking and other occupational injuries supports the hypothesis that modifiable risk factors can be identified to ultimately reduce the occurrence of UE trauma in the meatpacking industry. Two Midwest pork processing facilities processing between 9,000 and 10,000 hogs per day will be studied. Workers reporting to plant-based occupational health clinics with a UE laceration will be recruited as cases and interviewed soon after the injury event. Case-crossovermethods will be used to evaluate the risk for UE laceration injuries in the presence of transient worker-related risk factors such as personal protective equipment use, rushing, working with an unfamiliar cutting task, and UE pain. For case-crossover analyses, cases will be asked about the injury event in the presence of stable and transient exposures in a control period well before the injury and compared to a risk period immediately preceding the injury. Case-control methods will be used to evaluate risk for UE laceration injuries in the presence of stable ergonomic/job design factors including staffing levels, working with dull knives, and history of safety training. For case- control analyses, cases will be matched to controls working in the plant at the same time the case was injured and risk factor exposures will be compared using conditional logistic regression, adjusting for fixed covariates such as age, education, handedness and laceration history. Use of the two methodologies is a comprehensive approach to studying a spectrum of potentially modifiable risk factors that can be translated directly into preventive intervention strategies to reduce laceration occurrence in this high risk industry.